Wind turbines are exposed to harsh climatic environments. They are oftentimes installed on sites with bad wind conditions having high medium wind speeds and high turbulence gusts. In these cases it might be necessary that the operation of a wind turbine has to be at least temporarily stopped or interrupted in order to avoid an overload of its components. In particular, the hydraulic controlled pitch system may be affected due to high oil temperatures and/or low hydraulic pressures caused by a high pitch activity under instantly changing climatic circumstances. However, interrupting the operation of a wind turbine is an expensive approach to solve this problem as only sparse electric power is produced.
US 2007/0057517 relates to a method for limiting loads in a wind turbine by using measured loads or wind speed to increase the minimum pitch angle for extended periods. The minimum pitch angle will be allowed to relax down to the default when load excursions diminish. The method will allow turbines to capture more energy by operating in higher wind speeds and/or utilizing larger rotors without additional loss of fatigue life. Yet, this method is not capable of detecting an overload of components of the wind turbine like the hydraulic pitch system for example due to a high pitch activity in rough climatic conditions.
U.S. Pat. No. 7,452,185 B2 discloses a blade pitch-angle control device including a memory unit in which predetermined parameters that affect the load fluctuation of blades, azimuth angles, and pitch-angle command values are stored in association with each other. An azimuth-angle detecting unit detects the azimuth-angle of each of the blades. A parameter-detecting unit detects the predetermined parameters. A command-value receiving unit receives pitch-angle command values for each of the blades from the memory unit. Thereby, the pitch-angle command values are being selected on the basis of the azimuth-angle of each blade detected by the azimuth-angle detecting unit and the predetermined parameters detected by the parameter-detecting unit. Further, a pitch-angle control command-value generating unit that generates pitch-angle controlled command-values for individually controlling the pitch-angle of each blade on the basis of the pitch-angle command-values and a common-pitch-angle command-value is provided. Still, a measure for avoiding the overload of components of the wind turbine due to a high pitch activity that is in harsh climatic conditions is not given.